Composite interbody device

ABSTRACT

A composite interbody device includes superior and inferior endplates with a plastic core molded therebetween. The core includes one or more features for permitting bone growth through the core. Each endplate includes a bone interface side coated with hydroxyapatite, for promoting bone on-growth. Pores in the bone interface sides permit bone in-growth. Core interface sides of the endplates include relatively larger pores for accepting molten material from the core, for example during injection molding, to enhance bonding of the endplates with the core. Each endplate has a central barrier layer for preventing the molten core material from extruding through the core interface pores into the bone interface pores, reserving the bone interface pores for bone in-growth. A method of manufacturing the composite interbody device is also disclosed.

RELATED APPLICATIONS

This application is a divisional of U.S. Ser. No. 12/697,871, filed 1Feb. 2010, and incorporated herein by reference.

BACKGROUND

Spinal fusion treatment is considered a standard of care for intractablelower back pain arising from degenerative disc disease and/or spinalinstability. Fusion includes immobilizing the painful spine segments andencouraging bone growth across the immobilized level. In the cervicalspine, anterior decompression and fusion is the gold standard.

Spine fusion was first performed without instrumentation using bonegrafts, the bone grafts often being obtained from the patient's own body(i.e., from the iliac crest). Instrumented fusion, using rods, plates,and screws, was initially developed to provide rigid stability to thespine while the implanted bone grafts fused across the treated level.Since then, fusion implants have become common, replacing bone grafts.

Conventional implants are designed to facilitate primarilythrough-growth, or fusion resulting from growth of bone through holes orchannels through the implants, for example in order to reach other bone.For example, Medtronic LT Cages® are thimble-like titanium device thatare packed with a collagen sponge soaked in rhBMP-2 (recombinant humanbone morphogenic protein 2). A pair of the cages are inserted betweenadjacent vertebrae to initiate bone growth through the cages.Conventional CFR-PEEK cages (carbon fiber reinforced PEEK plastic cages)also rely upon through-growth—for example, the Jaguar™ and Saber™ LumbarI/F CAGE Systems house autologous cancellous bone grafts that growthrough the cages to join with adjacent vertebrae. Alphatec Novel TLspacers are made of PEEK plastic and include an internal chamberallowing for growth of bone therein.

Although effective, through-growth occurs slowly, for example, over aperiod of a year or more. Through-growth can be further delayed if theimplant area is not immobilized. Even micro-motion of the implant areacan disturb and disrupt bone growth, leading to increased incidence ofsubsidence and pseudarthrosis.

Some conventional devices attempt to improve implant stabilization byencouraging bone on-growth—a comparatively rapid, planar growth of boneupon surfaces of an adjacent implant, or upon surfaces of adjacent bone.For example, on-growth may be encouraged by coating a titanium cage witha chemical such as hydroxyapatite, a mineral naturally found in bone, toencourage new-grown bone to stick to the implant surface (for example,as is done with titanium dental implants). However, because they areradio-opaque, titanium cages and implants may hinder diagnosticassessment of bone growth, whether coated with hydroxyapatite or not.For example, implants made primarily of radio-opaque titanium mayobscure visualization of bone growth (e.g., through-growth) on x-rays.Titanium may likewise cause signal artifact with MRIs or CTs, making itdifficult to determine if fusion has occurred.

In order to avoid the visualization problems of titanium implants,attempts have been made to mix hydroxyapatite with, or applyhydroxyapatite to, radiolucent PEEK plastic (or other non-scatteringbiocompatible material, e.g., HDPE) to form a cage/implant. However,hydroxyapatite content embrittles the material and weakens suchimplants. In addition, PEEK provides poorer fixation than titanium, andthus, PEEK implants must often be supplemented with posterior pediclescrew and rod instrumentation.

SUMMARY

The interbody device described herein advances the art of fusion devicesby incorporating features to encourage simultaneous on-growth,through-growth and in-growth of bone (in-growth of bone beingcharacterized by bone growing into and around porous implant surfacefeatures). Facilitating all three types of bone growth results in fasterspinal or other bony fusion. Bony on-growth onto device surfacesprovides relatively quick, albeit limited mechanical rigidity. Next,in-growth, as achieved with the device described herein, incrementallyincreases mechanical strength as bone grows into porous features of theinterbody device to anchor bone to the device. Finally, bonythrough-growth, which takes the longest to complete, fully stabilizesand completes the fusion. On-growth and in-growth enhance devicestabilization, thus accelerating complete fusion by minimizingmicro-motion that could disrupt through-growth.

The interbody device described herein is primarily discussed in terms ofa PEEK plastic core or preexisting interbody device (such as anartificial disc) with metallic endplates. Titanium endplates arediscussed in depth; however, it will be appreciated that otherbiocompatible metals, as well as alternate core or preexisting devicematerials, may fall within the scope hereof.

In one embodiment, a composite interbody device includes a plastic corewith superior and inferior surfaces and one or more features forpermitting bone growth through the core. A superior endplate has a coreinterface side coupled with the superior surface. The superior endplatehas a bone interface side opposite the core interface side, forinterfacing with bone of an implant site. The bone interface sideincludes multiple bone interface pores for permitting bone growththerein. A metallic inferior endplate includes a core interface side anda bone interface side opposite the core interface side. The coreinterface side couples with the inferior surface of the core. The boneinterface side interfaces with bone of an implant site and includes boneinterface pores for permitting bone growth therein. A hydroxyapatitecoating applied to the bone interface sides of the superior and inferiorendplates encourages bone growth onto the endplates.

In another embodiment, a composite interbody device includes a superiorendplate, an inferior endplate and a core between the superior andinferior endplates. The superior endplate and the inferior end plateeach have a hydroxyapatite-coated, porous bone interface side forcontacting bone of an implant site. The hydroxyapatite coatingencourages bone growth onto the bone interface side, and pores of thebone interface side permit bone growth into the bone interface side. Thesuperior and inferior endplates each have a porous core interface sideopposite the bone interface side, a central barrier layer between thecore interface side and the bone interface side; and at least oneaperture through the endplate. The plastic core has a superior surfacebonded with and penetrating pores of the superior endplate coreinterface side; and an inferior surface bonded with and penetratingpores of the inferior endplate core interface side. At least one channelthrough the core is aligned with the superior endplate aperture and withthe inferior endplate aperture, the channel thus providing a pathway forthrough growth of bone through the interbody device.

In another embodiment, a composite interbody device has a plastic corewith superior and inferior surfaces and one or more features forpermitting bone growth through the core. A superior endplate includes acore interface side configured with the superior core surface, and abone interface side opposite the core interface side, for interfacingwith bone of an implant site. The bone interface side is coated withhydroxyapatite and has multiple micro-machined surface features forincreasing the bone interface side surface area to enhance bondingbetween bone and the superior endplate. An inferior endplate has a coreinterface side configured with the inferior core surface and a boneinterface side opposite the core interface side for interfacing withbone of an implant site. The bone interface side is coated withhydroxyapatite and has multiple micro-machined surface features forincreasing the bone interface side surface area to enhance bondingbetween bone and the inferior endplate.

In another embodiment, a method of manufacturing a composite interbodydevice includes assembling superior and inferior endplates by forming asolid central barrier layer on a bone interface layer, opposite a boneinterface side of the bone interface layer. A porous core interfacelayer is formed on the central barrier layer opposite the bone interfacelayer. The inferior and superior endplates are placed in a mold, on eachside of a core cavity, with the core interface layers facing the corecavity and the bone interface sides facing away from the cavity. Moltenplastic is injection-molded into the core cavity, to form a plastic corebetween the endplates and bonded with core interface sides of the coreinterface layers. The molten plastic extrudes into pores of the coreinterface layers to bond with the endplates.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a composite interbody device withsuperior and inferior endplates, according to an embodiment.

FIG. 2 is a cross-sectional view through the interbody device of FIG. 1.

FIG. 3 is a side view of the interbody device of FIG. 1.

FIG. 4 is a top view of the interbody device of FIG. 1.

FIG. 5 is a top view of the superior endplate of FIG. 1, showing a boneinterface side.

FIG. 6 is a side view of the superior endplate of FIG. 5.

FIG. 7 is a bottom view of the superior endplate of FIG. 65, showing acore interface side.

FIG. 8 is a perspective view of the superior endplate of FIG. 5.

FIG. 9 is a bottom view of the inferior endplate of FIG. 1.

FIG. 10 is a side view of the inferior endplate of FIG. 9.

FIG. 11 is a top view of the inferior endplate of FIG. 9, showing a coreinterface side.

FIG. 12 is a perspective view of the inferior endplate of FIG. 9.

FIG. 13 is a schematic view of a bone interface layer of the superior orthe inferior endplate of FIG. 1.

FIG. 14 is an enlarged view of an area of the bone interface layer ofFIG. 13.

FIG. 15 is a schematic view of a core interface layer of the superior orthe inferior endplate of FIG. 1.

FIG. 16 is an enlarged view of a section of the core interface layer ofFIG. 15.

FIG. 17 is a sectional view through the core interface layer of FIG. 15.

FIG. 18 is an enlargement of a portion of the sectional view of FIG. 17.

FIG. 19 is an exploded view showing layers forming an endplate of FIG.1, according to an embodiment.

FIG. 20 is a top view of the endplate of FIG. 19, showing an outermostbone interface layer.

FIG. 21 is a sectional view through the endplate of FIGS. 19 and 20.

FIG. 22 is an enlargement of a portion of the sectional view of FIG. 21.

FIG. 23 is an exploded view of a composite interbody device havingmachine-featured superior and inferior endplates, in accordance with anembodiment.

FIG. 24 is a perspective view of the composite interbody device of FIG.23, as assembled.

FIG. 25 is a side view of the assembled interbody device of FIG. 24.

FIG. 26 is a bone-side view of the superior or inferior endplate ofFIGS. 23 and 24.

FIG. 27 is an insertion end view of the device of FIG. 24.

FIG. 28 is an exploded perspective view showing composite layers formingthe endplates of FIG. 1 as applied to an artificial disc, according toan embodiment.

FIG. 29 is a flowchart showing a method of forming an interbody device,according to an embodiment.

FIG. 30 is a flowchart illustrating another method of forming aninterbody device, according to an embodiment.

FIG. 31 is a flowchart showing a method of forming an interbody device,according to an embodiment.

FIG. 32 is a flowchart showing a method of forming an interbody device,according to an embodiment.

FIG. 33 is a flowchart illustrating a further method of forming aninterbody device, according to an embodiment.

FIG. 34 is a simplified exploded, perspective view of a compositeinterbody device with superior and inferior endplates, according to anembodiment.

FIG. 35 is an end view of the device of FIG. 34.

FIG. 36 is a perspective view of the superior endplate of FIG. 39.

FIG. 37 is an end view of the endplate of FIG. 41.

FIG. 38 is a top view of the endplate of FIG. 36.

FIG. 39 is an enlarged view of a section of the endplate shown in FIG.38.

FIG. 40 is perspective view of the assembled device of FIG. 34,including post-assembly, machined features, according to an embodiment.

FIG. 41 is an exploded view of the device of FIG. 40.

FIG. 42 is a side view of the device of FIG. 40.

FIG. 43 is a top view of the device of FIG. 40, showing additionaldetail of a superior endplate.

FIG. 44 is an enlarged view of a section of the device shown in FIG. 43.

FIG. 45 is a perspective view of a composite interbody device havingsuperior and inferior endplates, according to an embodiment.

FIG. 46 is a second perspective view of the device of FIG. 45.

FIG. 47 is an exploded view of the device of FIGS. 45-46.

FIG. 48 is a side view of the device of FIGS. 45-47.

FIG. 49 is a cross-sectional view through the device of FIG. 48.

FIG. 50 is a top view of the superior endplate of the device of FIGS.45-47, showing a bone interface surface.

FIG. 51 is an end view of the device of FIGS. 45-47.

FIG. 52 is a side view of the device of FIGS. 45-47, showing a lateralchannel for bone through-growth.

DETAILED DESCRIPTION

FIG. 1 shows a composite interbody device 100 including a superiorendplate 102 and an inferior endplate 106, flanking a core 104. Core 104is for example a PEEK core (i.e., injection molded thermosetting PEEKplastic) having one or more features 108, such as channels through core104, for encouraging bone growth through device 100, and/or for housinga fusion enhancing material such as bone and any associated growthenhancers, or a fusion enhancing glue. Core 104 may alternately be madeof any other biocompatible material that is sufficiently malleable forforming in a desired shape, yet strong enough to meet durabilityrequirements of an intended implant site. Features 108 may be machinedafter core 104 is injection molded, or features 108 may be extruded orotherwise formed. Feature 108A is a vertically-oriented channel thatruns top-to-bottom through core 104, which aligns with an aperture 110in superior endplate 102 and an aperture 112 through inferior endplate106, when endplates 102 and 106 are assembled with core 104. Alignmentof aperture 110, channel 108A and aperture 112 together form a passagethat allows bone growth entirely through device 100. Because PEEK isradiolucent, core 104 may include one or more radio markers 114 forfacilitating visualization of core 104 on x-ray during or afterimplantation.

Feature 108B is a horizontally-oriented aperture or hole in a side ofcore 102, or alternately, a channel that runs side-to-side through core104. Feature 108C (labeled in FIG. 2) is a horizontally-orientedaperture or hole in a back side (distal to the spinal cord when insertedbetween vertebrae) of core 104, or alternately, a channel that runsback-to-front through core 104. In one embodiment, features 108B and108C open into vertically-oriented channel 108A, thus permitting bonegrowth through the sides and back of device 100, in addition to verticalbone growth through channel 108 and endplate apertures 110 and 112.Features 108A-C may be created by machining after core 104 is molded(e.g., after injection-molding core 104 between endplates 102 and 106.Alternately, features 108A-C may be molded into device 100 by use of oneor more removable mandrels placed in a mold for forming device 100.

As shown, endplates 102/106 are curved to conform to an accepting bonysurface, as further described with respect to FIG. 3, below. When core104 is molded between endplates 102 and 106, device 100 for exampleassumes a bullet shape that facilitates insertion into an implant site.It will be appreciated that endplates 102 and 106 may be straight,curved, angulated or otherwise shaped, depending upon the intendedapplication (i.e., the intended implant site or intended final shape ofdevice 100). Endplates 102 and 106 are for example diffusion bonded in apress, to achieve a desired shape and/or contour.

Endplates 102/106 are for example porous titanium coated withhydroxyapatite (HA), to encourage both bone on-growth (onto the porousendplates) and in-growth (into pores of the endplates). Coating titaniumendplates, rather than a PEEK core directly, with HA promotesbioactivity (e.g., bone growth) without sacrificing strength andtoughness of core 104. Titanium is a biocompatible material that bondswith HA and therefore facilitates bone on-growth with endplates 102 and104. Titanium HA coated endplates provide strength, biocompatibility andon-growth without compromising the strength of the PEEK core as occurswhen HA is blended directly into PEEK (PEEK fracture toughness is knownto be degraded with direct application of HA). In addition, thetitanium-PEEK-titanium combination of device 100 avoids the greaterstiffness of a primarily titanium implant, thereby reducing stressshielding that inhibits bone growth and bone fusion. It will beappreciated that other biocompatible metals such as molybdenum,cobalt-chrome, stainless steels and other biocompatible alloys, may beused in place of or in addition to titanium in forming endplates 102 and106. For example other biocompatible metals may be alloyed with titaniumto form endplates 102 and 106.

FIG. 2 is a rear view of device 100, featuring endplates 102 and 106configured with core 104 and showing rear feature 108C. Rear feature108C is an aperture in core 104 having dimensions of about 4 mm wide by3-6 mm high. In addition to permitting bone growth through the back endof core 104, feature 108C facilitates placement of device 100 at animplant site by use of a tool sized to fit feature 108C.

In one aspect, height (h_(D)) of device 100, including endplates 102 and106, ranges from about 12 mm to about 17.1 mm. When aligned with channel108A, aperture 110 of superior endplate 102 and aperture 112 of inferiorendplate 106 may open into common space within core 104, which is alsoaccessible via at least feature 108C.

FIG. 3 is a side view of assembled device 100. In one aspect, device 100includes superior and inferior endplate contact surfaces 116 and 118,spanning at least a portion of the length (l_(D)) of device 100/core104. Length l_(D) is for example about 26 mm Endplates 102/106 arecurved to conform with a shape of contact surfaces 116 and 118. Althoughnot shown in FIG. 3, it will be appreciated that endplates 102 and 106may also be shaped on bone interface sides 126, opposite the endplatecontact surfaces, to conform or optimally interact with bony surfaces ofan intended insertion site. Core 104 may be beveled starting at a bevelline 120 to a nose 122, to facilitate insertion between bony surfacessuch as adjacent vertebrae. Device 100 is for example insertednose-first between vertebrae in the direction indicated by insertionarrow 124. Endplates 102/106 have an endplate height (h_(E)) of betweenabout 1-2 mm. Endplates 102/106 may be coated with hydroxyapatite beforeor after assembly with core 104. In one example, endplates 102/106 arespray coated with hydroxyapatite prior to placement in a mold, and core104 is injection molded between endplates 102/106.

FIG. 4 is a simplified top view of device 100 showing bone interfaceside 126 of superior endplate 102, described further with respect toFIGS. 5-8. It will be appreciated, after reading the followingdescription, that FIG. 4 may also represent a bone interface side ofinferior endplate 106.

In an embodiment according to FIGS. 4-8, device 100 width (w_(D)) isabout 11 mm. Aperture 110 of endplate 102 has an aperture length (l_(A))of about 13-14 mm and an aperture width (w_(A)) of about 5-6 mm (FIG.4). Endplate 102 has a superior endplate length (l_(ES)) of about 22-23mm (FIG. 5). Bone interface side 126 of endplate 102 is for exampleHA-coated titanium, molybdenum or other biocompatible metal, whichincludes a plurality of holes or pores 127 into which bone may grow whendevice 100 is implanted. Bone interface side 126 is opposite a coreinterface side 128 (FIG. 6). Core interface side 128 faces core 104 andincludes a plurality of holes or pores 129 for accepting material ofcore 104 to enhance adhesion to core 104. Pores 127 of bone interfaceside 126 are of optimal size for promoting bone in-growth. For example,pores 127 are about 600 microns in diameter. Pores 129 of core interfaceside 128 are larger than the pores 127 of bone interface side 126, tomaximize bonding between core 104 and endplate 102. When injectionmolded between endplates 102 and 104, core 104 material penetrates coreinterface side 128 via the larger pores 129, to firmly bond endplate 102with core 104. Pores 127 and 129 may be perforations or holes throughsides 126 and 128, respectively, or pores 127 and 129 may be openings ina wire mesh forming sides 126 and 128. The terms pores, perforations andopenings are used interchangeably, below.

Superior endplate 102 and inferior endplate 106 are curved or otherwiseshaped for ease of insertion. However, endplates 102 and 106 mayalternately be shaped to maximize contact between device 100 andadjacent bone (for example, endplate bone-interface sides 126 may beflattened to maximize surface area contact between endplates 102/106 andadjacent bone). As shown in FIGS. 1, 3, 8 and 12, endplates 102 and 106are curved to mate with accepting vertebral surfaces at an implant site.The shape of device 100 therefore mimics an intervertebral space. Shapeand size of device 100 and endplates 102/106 and/or core 104 may bealtered to suit differently sized and shaped implant sites. Device 100may be shaped to mimic a cavity created by a cutting tool used toprepare an implant site. For example, device 100 may be shaped to mimica cavity reamed out by a ball mill to facilitate fusion at a hip, kneeor shoulder joint.

FIGS. 9-12 show additional detail of inferior endplate 106, and are bestviewed together with the following description. Like endplate 102,endplate 106 has a bone interface side 126 with pores 127 (that are forexample about 600 microns) and a core interface side 128 with relativelylarger pores 129 for accepting core 104 material. Bone interface side126 may be hydroxyapatite-coated titanium, molybdenum or otherbiocompatible metal. Aperture 112 may be created by machining aftermolding, and is sized to permit access to vertically-oriented channel108A of core 104, for example having dimensions similar to aperture 110of superior endplate 102. Endplate 106 may be slightly shorter thanendplate 102, having an inferior endplate length (l_(EI)) of about 21-22mm. Endplates 102/106 are, for example, fabricated from a large sheet ofbone interface side 126 material backed by core interface side 128material that is cut into multiple endplates, which are then shaped asdesired. For example, sheets of core interface side 126 material andbone interface side 128 material may be preliminarily bonded and cutinto desired sizes for forming endplates 102/106. The cut sections maythen be diffusion bonded to permanently join side 126 material with side128 material at a molecular level, under heat and pressure. Endplates102/106 may be curved or otherwise shaped as desired during or prior todiffusion bonding. As described below with respect to endplate assembly200 (FIG. 19), a central barrier layer is inserted between side 126material and side 128 material, to prevent core material that penetratespores 129 of core interface side 128 from seeping into or clogging bonein-growth areas provided by pores 127 of side 126.

FIG. 13 is a top view of bone interface side 126 of endplate 102/106,and FIG. 14 shows additional detail of a section A of side 126. In oneembodiment, bone interface side 126 is a thin sheet of titanium, andpores 127 are perforations through bone interface side 126. Perforations127 have a diameter of about 0.30 mm and a center-to-center spacing ofabout 0.050 mm along a given row 130 or 132. For example, a distancefrom the center of perforation 127A to the center of perforation 127B inrow 132 is about 0.30 mm. Perforations 127 of adjacent rows 130 and 132are offset such that a center-to-center (diagonal) distance betweenperforation 127A in row 132 and perforation 127C in row 130 is about0.030-0.045 mm Perforations 127 may commence about 0.030-0.040 mm fromedges of bone interface side 126.

As illustrated in FIGS. 15-18, in one embodiment, pores 129 of coreinterface side 128 are perforations through a thin sheet of titanium orother metal. Perforations 129 are optimized for accepting material ofcore 104 when core 104 is injection molded between core interface sides128 of endplates 102/106. Perforations 129 are larger than pores 127,and may be elliptical to rectangular in shape. In one aspect,perforations 129 have a width (w_(P)) of about 0.050 mm and a length(l_(P)) of about 0.100 mm. Perforations 129 are for example spaced atabout 0.050 mm from edges of side 128 and adjacent perforations arespaced about 0.010 mm apart.

FIG. 17 is a cross-sectional view of side 128, taken along line 17-17 ofFIG. 15. FIG. 18 is an enlarged view of section B of FIG. 17, showing aside view of perforations 129.

FIG. 19 is an exploded view of an assembly 200 for forming endplate 102and/or endplate 106 of interbody device 100, described above. FIG. 20illustrates a bone interface side view of assembly 200. FIG. 21 is across-sectional illustration taken along line 21-21 of FIG. 20, and FIG.22 is an enlarged view of a portion C of FIG. 21, showing additionaldetail of assembly 200 in cross-section. FIGS. 19-22 are best viewedtogether with the following description.

In an embodiment according to FIGS. 19-22, assembly 200 includes a boneinterface side 202 including at least two bone interface layers 204 and206. First and second bone interface layers 204 and 206 are shown inFIG. 19. Additional bone interface layers (e.g., for a total of four tofive layers) may be added, to vary bone in-growth characteristics ofside 202 and/or tensile strength or other characteristics of endplate102 or 106 formed from assembly 200.

First and second layers 204 and 206 are for example coated withhydroxyapatite to encourage bone on-growth, and are formed of titaniumwire mesh of an optimal size for bone in-growth (e.g., the mesh providespores 208 of about 600 microns diameter). The wire of the mesh is forexample 0.5 mm titanium wire, and provides relatively low porosity andrelatively high flow restriction as compared with a core interface side210. Pores 208 may alternately take on a square, rectangular or othershape having minor dimensions of about 600 microns (e.g., the width of arectangular pore) and major dimensions of no more than approximatelythree times the minor dimensions (e.g., the rectangular pore is nolonger than about 1800 microns).

Core interface side 210 lies opposite bone interface side 202 andincludes at least one core interface sheet 212 of titanium or otherbiocompatible metal. Sheet 212 includes perforations or pores 214 thatare larger than pores 208 of side 202, to maximize bonding between anendplate formed with assembly 200 and an interbody core such as core104, or another interbody device, such as an artificial disc.

Core interface sheet 212 may be a mesh formed with larger-gauge wirethan the mesh of layers 204 and 206, or with a looser-weave mesh toprovide relatively larger pores, higher porosity and lower flowrestriction than side 202. Higher porosity and lower flow restrictionenhance flow of material from an interbody core/device (i.e., core 104material) into pores 214 of side 210, to encourage bonding between anendplate (i.e., endplate 102/106) formed with assembly 200 and thecore/device. It will be appreciated that although a single sheet 212makes up core interface side 210 in FIG. 19, side 210 may includemultiple sheets 212 of larger-gauge titanium wire mesh.

Alternately, side 210 includes one or more perforated or micro-etchedcore interface sheets 212 with pores sized to encourage bonding betweenan endplate (e.g., endplate 10/106) formed with assembly 200 and aninterbody core/device. A central plate or layer 216 between side 202(layers 204 and 206) and side 210 (sheet 212) prevents material from theinterbody core/device (e.g., PEEK of core 104) from over-extruding intoendplate 102/106. Central layer 216 for example prevents PEEK or othercore 104 material from flowing all the way through endplate 102/106,blocking the plastic from flowing into bone interface layers 204 and 206and thus maintaining the bony in-growth spaces provided by pores 208.

Assembly 200 is diffusion bonded, by placing layers 204, 206, 212 and216 into a die and applying heat and pressure to create an artificialporous matrix. Diffusion bonding at an atomic level facilitatescombination of surfaces that touch one another, and results in near 100%bonding. Diffusion bonding may occur prior to forming endplates 102/106from assembly 200. For example, assembly 200 may be formed as a 50 mm by25 mm by 0.75 mm composite sheet (or an alternately sized compositesheet), and endplates 102/106 may be cut from assembly 200 afterdiffusion bonding. Alternately, endplates 102/106 are cut from assembly200 (which may be preliminarily bonded) or assembly 200 is sized to therequirements of endplates 102/106, prior to diffusion bonding. Sincediffusion bonding does not require flat sheets, unique curvatures ofeither or both endplates 102/106 are accommodated. Curvature may beintegrated into dies for diffusion bonding to allow customization ofendplates 102/106 for any interbody device/core (such as core 104)and/or any accepting bony surface. For example, endplates 202 and 206may be diffusion bonded in a press to produce a desired endplate shapeor contour. During manufacture, endplates 102/106 may also be mirroredor trimmed to suite multiple sizing requirements.

In one embodiment, dual assemblies 200 are sized according to sizingrequirements for endplates 102 and 106. Assemblies 200 are positionedinto a mold with core interface sides 210 facing a cavity for corematerial (e.g., core 104 material or material for forming an artificialdisc or another interbody device configured for bonding with endplates102/106). Core material (e.g., PEEK) is injection molded betweenassemblies 200 and penetrates pores 214 of core interface side 210, tofirmly bond with assembly 200 (endplates 102/104). Central layer 216prevents core material from over-extruding into pores 208 of layers 204and 206, thus preserving bone in-growth spaces of bone interface side202. As shown in FIG. 22, pores 208 of layers 204 and 206 may beselectively offset to optimize side 202 for bone in-growth.

Once set, the shape and geometry of the interbody core/device (e.g.,core 104) may be refined by machining out of composite blanks. Forexample, features 108 are machined into core 104 after molding (see FIG.1). Hydroxyapatite is surface treated onto bone interface side 202 ofendplates 102/106, before or after core 104 is injection moldedtherebetween, to promote bone on-growth and in-growth onto and into boneinterface side 202. Hydroxyapatite may be spray-coated, painted orotherwise applied to bone interface sides 202. Depth of thehydroxyapatite coating may be varied to achieve optimalon-growth/in-growth efficiency, or according to an intended implantlocation. The metal-PEEK-metal (e.g., titanium-PEEK-titanium)combination of device 200 is less stiff than a primarily titaniumimplant and thus reduces stress shielding.

In one embodiment, titanium sheets formed with perforations and/ortexture replace the mesh forming one or both of layers 204 and 206.Layers 204 and 206 may be selectively micro-perforated or photo etchedto provide pores 208 and/or other texturizing features. For example,layers 202 and 204 are etched with 500 micron (40-mil)perforations/pores 208 using a photo etching process capable of aresolution of 5 mil (0.125 mm). Side 202 may thus be formed as a matrixof sequentially stacked titanium perforations/pores 208. Selectiveplacement of titanium perforations/pores 208 on side 202 and largerpores 214 on side 210 allows porosity control for regulating/encouragingboth bone in-growth and PEEK bonding. For example, porosity may becontrolled to produce pores 208 of approximately 500-600 microns, forideal bone in-growth.

FIGS. 23-26 show an interbody device 300 having machine-featuredsuperior and inferior endplates 302 and 306, flanking a core 304. Core304 may be similar to core 104 of FIG. 1. Core 304 includes multiplefeatures 308, such as vertically-oriented channel 308A runningtop-to-bottom through core 104, and a horizontally-oriented channel 308Brunning side-to-side through core 104. Features 308A and 308B facilitatebone growth through core 304/device 300, and may be packed with boneand/or other materials to enhance fusion (e.g., proteins or othermaterials to enhance bone growth, or fusion enhancing glues). A slot308C in a back side (distal to the spinal cord when inserted betweenvertebrae) of core 304 is sized to fit an insertion tool, to facilitateinsertion of device 300 between adjacent vertebrae. Features 308A-C maybe machined after core 304 is molded (e.g., after injection-molding core104 between endplates 302 and 306) or features 308A-308C may be extrudedor otherwise formed.

Channel 308A aligns with an aperture 310 in superior endplate 302 andwith an aperture 312 in inferior endplate 306 when device 300 isassembled as shown in FIG. 24. It will be appreciated that any fusionaids for insertion into device 300 may be loaded via aperture 310 oraperture 312. Where core 304 is formed of radiolucent material, such asPEEK plastic, one or more radio markers 314 may be incorporated tofacilitate visualization of core 304 on x-ray, for example once device300 is implanted. Endplate 302 bonds with a superior endplate contactsurface 316 of core 304, and endplate 306 bonds with an inferiorendplate contact surface 318, as shown in FIG. 25. Core 304 may taperfrom a bevel line 320 to a nose 322, to facilitate insertion of device300 into an intervertebral space or other implant site.

Endplates 302 and 306 are curved as a result of forming and diffusionbonding in a press to conform to a desired shape of core 304 and/or anaccepting bony surface. In one aspect, endplates 302 and 306 aremulti-surface machined yielded titanium plates with geometric featuresprotruding therefrom, to increase relative endplate surface area forbone on-growth on bone interface sides 326 (see FIG. 25). Ridges 313 areshown in FIGS. 23-27 for ease of illustration; however, it will beappreciated that ridges 313 are representative only and may be replacedor supplemented by thin webs or other geometries. For example, endplates302 and 306 may bear geometric features resulting from fracturing (i.e.,pulling apart) a titanium plate. Such endplates may advantageously beformed in a one-step manufacturing process, thereby reducing overallcost of the interbody device.

Alternately, although not shown, core interface sides 328 of endplates302 and 306 may also bear geometric features for increasing surface areaof core interface sides 328 to enhance bonding with core 304 material.Alternately, a porous titanium layer, such as sheet 212 (see FIG. 19)may be diffusion bonded with a back (un-featured) surface of a singletitanium sheet having ridges 313 or other features on its opposite side.For example, core interface side 328 may include a sheet of titaniumwire mesh or perforated titanium that is diffusion bonded with a backsurface of bone interface side 326. In such configuration, no centralbarrier layer is required.

Device 300 length (l_(D300)) and height (h_(D300)), shown in FIG. 25,are for example similar to length (l_(D)) and height (h_(D)) of device100 (see FIGS. 2-3). Device 300 width (w_(D300)), shown in FIG. 26, mayalso be similar to width (w_(D)) of device 100.

FIG. 28 is an exploded perspective view of an interbody device 400,showing composite layers forming superior and inferior endplates 402 and406, as applied to an artificial disc 404. In one embodiment, endplates402 and 406 each include bone interface layers 405 and 407 selectivelyplaced, one layer relative to the other, to optimize bone in-growthspaces provided by pores or perforations 408 of layers 405 and 407. Adisc interface layer 412, having relatively larger pores 414 (ascompared with pores 408), is separated from layers 405 and 407 by acentral barrier layer 416 that is for example a thin sheet of solidmetal. Larger pores 416 admit flow of artificial disc 404 materialtherein. For example, molten or softened plastic forming disc 404 mayextrude into pores 414 to maximize contact and bonding between disc 404and layer 412, and thus between disc 404 and endplates 402 and 406.Central barrier layer 416 prevents material of disc 404 from flowinginto pores 408, thus reserving pores 408 for bone in-growth.

Bone interface layers 405 and 407, disc interface layer 412 and centralbarrier layer 416 are made of a biocompatible metal such as titanium. Inone embodiment, bone interface layers 405 and 407 are HA-coated titaniumwire mesh having pores 408 formed by spaces between small gauge (e.g.,0.5 mm) titanium wire. However, a perforated, HA-coated titanium sheetmay replace one or both of bone interface layers 405 and 407. Centralbarrier layer 416 is a solid sheet of titanium, and core interface layer414 is a sheet of titanium mesh having larger pores than bone interfacelayers 405 and 407, to enhance bonding with artificial disc 404.

Endplates 402 and 406 may be applied layer-by-layer to superior andinferior endplate contact surfaces 417 and 418 of core 404. For example,disc interface layer 412 is first applied to superior endplate contactsurface 417. Central barrier layer 416 is applied to layer 412, andtitanium/HA bone interface layers 407 and 405 are applied to centralbarrier layer 416. Layers 405 and 407 may be selectively placed tooptimize interface between sheets, and to optimize porosity (i.e.,alignment of pores 408 of each layer 405, 407) for bone in-growth.Although not shown, layers 405 and 407 may themselves each includemultiple sublayers (e.g., 4-5 sublayers) of titanium wire mesh toprovide further lower porosity and raise flow restriction. Contactsurfaces 417 and 418 may be PEEK plastic, titanium, cobalt chrome oralloy surfaces of artificial disc 404, the remainder of which may beconfigured of the same material or an alternate material as contactsurfaces 417 and 418. Any of bone interface layers 405, 407 and centralbarrier layer 416 may be diffusion bonded to one another or to discinterface layer 412. Where artificial disc 404 includes metallic contactsurfaces 417 and 418, all layers of endplates 402 and 406 may bediffusion bonded directly to the metallic contact surfaces.

Artificial disc 404 may also be molded between pre-assembled endplates402, 406, as described above with respect to core 104 of interbodydevice 100.

Layers 405, 407, 416 and 412 may optionally be pre-formed into singlecomposite endplates 402/406 that are shaped (i.e., via simultaneousforming and diffusion bonding in a press) to complement respectivecontact surfaces 417 and 418, and that are applied in single operationsto superior endplate contact surface 417 and to inferior endplatecontact surface 418. One exemplary disc suitable for application oflayers 405, 407, 416 and 412 (or endplates 402/406 formed therefrom) isa Pioneer NuBak PEEK on PEEK disc. Endplates 402 and 406 may be shapedto compliment a shape of disc surfaces 417 and 418, or disc 404 may beinjection molded between the endplates, with disc 404 conforming to theshape of the endplates.

FIG. 29 illustrates one method 500 for forming an interbody device, suchas device 100. Inferior and superior endplates are assembled, in step502, and placed in a mold with core interface layers facing a corecavity, in step 504. Core material is injection molded into the cavityand, through the cavity, into pores of the core interface side, in step506. In one example of steps 502-506, endplates 102 and 106 areassembled as described with respect to FIG. 19 (assembly 200). Theendplate-core-endplate assembly is allowed to set (for example, theassembly may be cooled until the core fully hardens), in step 508, andremoved from the mold, in step 510. Features are formed in the interbodydevice, in step 512. In one example of step 512, features 108A-108C andapertures 110 and 112 are formed in device 100. For example, one channelmay be drilled through device 100 to form aperture 110, channel 108A andaperture 112. Bone interface surfaces of the device (i.e., boneinterface surfaces 126, see FIG. 3) are coated with hydroxyapatite, instep 514. It will be appreciated that although shown as a final step inFIG. 29, hydroxyapatite may alternately or additionally be coated ontobone interface surfaces prior to their incorporation into endplates 102and 106, or after formation of the endplates and prior to placement inthe mold.

FIG. 30 shows a method 600 for forming an interbody device. Method 600is for example used to form device 100, with an assembly such asassembly 200 used to form endplates 102 and 106. A central barrier layeris formed on a core interface side, in step 602, and a bone interfaceside formed on the central barrier layer, opposite (e.g., on an oppositeside from) the core interface side, in step 604. In one example of steps602-604, central layer 216 is placed on core interface side 210, andbone interface side 202 is placed on central layer 216 (FIG. 19). Ifshaping is required (decision 606), for example if endplates such asendplates 102 and 106 are to be cut from a larger assembly of sides 202and 210 and central layer 216, then endplates are shaped from theassembly, in step 608. The endplates are diffusion bonded, in step 610,and placed into a mold with core interface sides facing a cavity, instep 612. In one example of steps 606-612, endplates 102 and 106 are cutfrom a larger master sheet of preliminarily bonded side 202, centrallayer 216 and core side 210, and diffusion bonded under heat andpressure, prior to placement in a mold having a cavity sized and shapedfor forming core 104. In another example, a master sheet of side 202,central layer 216 and core side 210 is diffusion bonded prior to cuttingor otherwise shaping endplates 102 and 106 from the master sheet. Theendplates are then placed into a mold as described.

In step 614, core material is injection-molded into the core cavity, andallowed to extrude into pores of the core interface side. The moldedassembly is allowed to set until hardened, in step 616, and removed fromthe mold, in step 618. Endplate and/or core features may be created inthe hardened interbody device, in step 620. In one example of steps614-620, material of core 104, such as molten PEEK plastic, is injectionmolded into the core cavity and allowed to extrude into perforations orpores 214. Central barrier layer 216 prevents the core 104 material fromextruding into pores 208 of side 202, thus reserving pores 208 as bonein-growth spaces. Once hardened, apertures 110 and 112 may be formed insuperior and inferior endplates 102 and 106 (respectively), and channel108A, channel 108B and aperture 108C may be formed in core 104. Forexample, apertures 110 and 112 and channel 108A may be formed in asingle drilling or other machining operation through interbody device100. Optionally, certain features of core 104 may be produced via aspecially shaped mold having one or more mandrels for producing passagesin the molten PEEK plastic.

FIG. 31 illustrates a method 700 of forming an interbody device, such asdevice 100, the endplates of which may be formed from assembly 200. Instep 702, titanium wire mesh is selectively layered to form a boneinterface side. A central barrier layer is formed from a solid titaniumsheet, on the bone interface side, and a core interface layer is formedfrom larger-weave titanium mesh, on the central barrier layer, in steps704 and 706. In one example of steps 704-706, bone interface side 202 isformed by selectively placing together titanium wire mesh layers 204 and206, such that the pores 208 formed by openings in the mesh are at adesired orientation, one layer relative to the other. Central layer 216,which is for example a solid titanium sheet, is placed with side 202,and at least one core interface sheet 212 is placed with the oppositeside of central layer 216, to form bone interface side 210. As notedabove, pores 214 of sheet 214 are larger than pores 208, to reduce flowrestriction on the core interface side.

The bone interface side, barrier layer and core interface side (e.g.,side 202, central layer 216 and side 210) are diffusion bonded together,in step 708. If shaping is required (decision 710), endplates (e.g.,endplates 102 and 106) are shaped from the bone interface side/barrierlayer/core interface side assembly, in step 712, and optionally coatedwith hydroxyapatite on their bone interface sides, in step 714. Step 714is illustrated as a dotted box to indicate that hydroxyapatite coatingmay take place at other points in method 700, for example at position726 or elsewhere.

The endplates are placed in a mold with their bone interface sidesfacing a core cavity, in step 716, and core material is injection moldedbetween the endplates, and allowed to extrude into the pores (e.g., meshopenings) in the core interface side, in step 718. After setting (Step720), the interbody device is removed from the mold, in step 722, andendplate and/or core features are created, in optional step 724. In oneexample of steps 716-724, endplates 102 and 106 are placed into a moldwith sides 210 facing an adjacent cavity. Molten material of core 104(e.g., PEEK plastic) is injected into the mold and allowed to penetratepores 214. After the PEEK is allowed to set, the rough interbody deviceis removed from the mold, and apertures 110 and 112 are formed inendplates 102 and 106, and any of features 108A-108C that were notformed in molding 104 are machined into core 104. For example, apertures110, 112 and channel 108A are drilled through device 100.

Bone interface sides (e.g., sides 202) are coated with hydroxyapatiteafter the interbody device is machined with its desired features, afterthe endplates are shaped from the bone interface side/barrier layer/coreinterface side assembly, or both. Alternately, mesh layers forming thebone interface side may be coated with hydroxyapatite prior to placingthe layers together to form the bone interface side, or the boneinterface side may be coated with hydroxyapatite prior to its placementwith the central barrier layer. The depth and placement ofhydroxyapatite coating may vary as a function of an intended implantsite.

FIG. 32 illustrates a method 800 of forming an interbody device. Method800 may be used to form device 100 using assembly 200 to make endplates102 and 106. A bone interface side is formed from at least one sheet ofperforated titanium, in step 802, and a central barrier layer formedfrom a solid sheet of titanium is placed on the bone interface side, instep 804. A core interface side is formed on the central barrier layer,opposite the bone interface layer, in step 806. In one example of steps802-806, bone interface side 202 is formed by selectively placing aplurality of perforated titanium sheets together such that theperforations are at a desired orientation, one layer relative to theother. See also FIGS. 5-8, showing perforated bone interface side 126with perforations 127.

Central layer 216, which is for example a solid titanium sheet, isplaced with side 202, and at least perforated titanium sheet 212 isplaced with the opposite side of central layer 216, to form boneinterface side 210. Perforations 214 of sheet 212 are larger thanperforations 208, to reduce flow restriction on the core interface side.

The bone interface side, barrier layer and core interface side (e.g.,side 202, central layer 216 and side 210) are diffusion bonded together,in step 808. If shaping is required (decision 810), endplates (e.g.,endplates 102 and 106) are shaped from the bone interface side/barrierlayer/core interface side assembly, in step 812, and optionally coatedwith hydroxyapatite on their bone interface sides, in step 814. Step 814is illustrated as a dotted box to indicate that hydroxyapatite coatingmay take place at other points in method 700, for example at position826 or elsewhere.

The endplates are placed in a mold with their bone interface sidesfacing a core cavity, in step 816, and core material is injection moldedbetween the endplates, and allowed to extrude into the pores (e.g., meshopenings) in the core interface side, in step 818. After setting (Step820), the interbody device is removed from the mold, in step 822, andendplate and/or core features are created, in optional step 824. Boneinterface sides are coated with hydroxyapatite in step 826, if notalready coated, or if additional coating is desired. Steps 816-826 aresimilar to steps 716-726, described in greater detail above.

FIG. 33 shows a further method for forming an interbody device, such asdevice 300. A porous core interface layer is placed on the back side ofa featured titanium sheet, in step 902, and the two are diffusion bondedtogether, in step 904.

In one example of steps 902-904, porous sheet 212 is placed on coreinterface side 328 of material forming endplate 302 or 306 (FIG. 24),and the porous sheet is diffusion-bonded with the material forming theendplate. Steps 902-904 provide for an endplate having a plurality ofmachined webs, ridges (e.g., ridges 313) or other surface-areaincreasing features for enhancing bone contact on the bone interfaceside, and pores on the core interface side for enhancing bonding withthe core.

Endplates are shaped from the diffusion bonded assembly if necessary(decision 906), in step 908. Bone interface sides are optionally coatedwith hydroxyapatite, in step 910, and the endplates are placed in a moldwith their core interface layers/sides facing a central cavity, in step912.

Core material is injection molded between the endplates, and allowed toextrude into the pores (e.g., mesh openings) in the core interface side,in step 914. After setting (Step 916), the interbody device is removedfrom the mold, in step 918, and endplate and/or core features arecreated, in optional step 920. Bone interface sides are coated withhydroxyapatite, in step 922, if not already coated, or if additionalcoating is desired. Steps 906-922 are similar to steps 712-726,described in greater detail above.

FIG. 34 shows a composite interbody device 1000 including a superiorendplate 1002 and an inferior endplate 1006, flanking a core 1004. FIG.35 is a simplified front view of assembled device 1000. FIGS. 36-39 showdetails of endplate 1002 of device 1000, prior to formation of threadingon endplate 1002. FIGS. 34-39 are best viewed together with thefollowing description.

Core 1004 is for example a PEEK core (i.e., injection moldedthermosetting PEEK plastic) having one or more features 1008, such aschannels through core 1004, for encouraging bone growth therethrough.Because PEEK is radiolucent, core 1004 may include one or more radiomarkers 1014 for facilitating visualization of core 1004 on x-ray,during or after implantation. Core 1004 may alternately be made of anyother biocompatible material that is sufficiently malleable for formingin a desired shape, yet strong enough to meet durability requirements ofan intended implant site. Radiomarkers 1014 may not be required wherecore 1004 is made of a radio-opaque material.

Features 1008 may be machined after core 1004 is injection molded, orfeatures 1008 may be extruded or otherwise formed with core 1004.Feature 1008A is shown with respect to FIG. 40, and described below.Feature 1008B is a horizontally-oriented channel that runs front-to-backthrough core 104. Features 1008C-1008E are horizontally-oriented,lateral openings into core 1004, or alternately, lateral channels thatrun through core 1004, generally perpendicular to channel 1008B andintersecting channel 1008B within core 1004. Channel 1008B accommodatesan insertion tool, such as a surgical drill, to facilitate placement ofdevice 1000 at an implant site. Channel 1008B may also allow bone growththrough device 1000, when device 1000 is implanted (e.g., betweenvertebrae to enhance spinal fusion, or at a hip socket to enhance hipfusion). For example, bone growing into device 100 via avertically-oriented slot 1008A through device 1000 (see FIG. 40 and itsdescription, below) may extend through channel 1008B.

Features 1008C-E accommodate fusion-enhancers such as glues, bone graftor other fusion enhancing materials, and/or permit bone growththerethrough. For example, bone growing within channel 1008A may branchinto features 1008C-E, where not fully filled with a fusion-enhancer.When implanted between adjacent vertebrae, features 1008B-E rungenerally perpendicular with a long axis of the spine.

As shown, device 1000 has a cylindrical shape with a relativelyconsistent diameter. Diameter d of device 1000 is for example about 20mm. However, it will be appreciated that the diameter of device 1000 mayvary from end to end, to facilitate insertion into a desired implantsite. For example, where implanted in an intervertebral space, device1000 may taper from an end 1007 distal to the spinal column, to aninsertion end 1005 that is proximal to the spinal column when device1000 is implanted. Endplates 1002/1006 (and optionally, core 1004, seeFIGS. 36-37) are threaded, to facilitate screwing device 1000 into animplant site. For example, device 1000 may be rotationally advanced intoa cavity left by a surgical drill, the cavity having a diameter slightlysmaller than diameter d. In one aspect, device 1000 is self tapping. Asdevice 1000 is screwed into place, for example into a cavity createdbetween adjacent vertebrae, threads 1015 decorticate bone of thevertebral endplates and provide bleeding bone edges to enhance bonegrowth onto and into device 1000. Threads 1015 may further allow forcontrolled widening of a collapsed disk space, to relieve pressure oncompressed nerve roots. In addition, threads 1015 increase surface areaof bone interface sides 1026 of endplates 1002 and 1006, for enhancedbone-to-device contact and bonding.

In one aspect, endplates 1002/1006 are threaded titanium, coated withhydroxyapatite (HA) to encourage both bone on-growth. It will beappreciated that other biocompatible metals such as molybdenum,cobalt-chrome, stainless steels and other biocompatible alloys, may beused in place of or in addition to titanium in forming endplates 1002and 1006. Pores 1027 penetrate bone interface sides 1026 of endplates1002 and 1006, providing a plurality of spaces for bone growth intoendplates 1002 and 1006. Core interface sides 1028 of endplates 1002 and1006 are shown as non-porous surfaces, preventing core 1004 materialfrom seeping into pores 1026 during bonding of core 1004 with endplates1002 and 1006. However, it will be appreciated that an endplateconfiguration with porous bone interface and core interface sides, witha barrier layer therebetween, may be incorporated into one or both ofendplates 1002 and 1006. Such a configuration is described above withrespect to endplate assembly 200 (illustrated in FIGS. 19-22).

Core 1004 may be injection molded between endplates 1002 and 1006 in amanner similar to that described above (see, e.g., FIG. 29 and thecorresponding description). Endplates 1002 and 1006 may be formed withthreads 1015 prior to injection-molding of core 1004 between theendplates. Optionally, endplates 1002 and 1006 are formed asnon-threaded, curved metallic sheets with pores 1027 penetrating boneinterface sides 1026. See, e.g., FIGS. 36-39, showing a non-threadedsuperior endplate 1002. In one aspect, threads 1015 and any additionalfeatures (such as features 1008 and endplate apertures, shown anddescribed with respect to FIGS. 40, 41 and 43) are machined into device1000 after injection molding and hardening of core 1004 betweenendplates 1002 and 1006.

Endplate 1002 has a length (l_(E1002)) of about 30 mm and a width(w_(E1002)) of about 17-18 mm (see FIG. 38). In one aspect, the lengthof device 1000 is also about 30 mm Endplate 1002 spans the length ofdevice 1000. As shown in FIG. 37, the radius (r) of device 1000 is about10 mm, whereas a distance (r₂) from the center (c) of core 1004 to coreinterface surface 1028 of endplate 1002 is about 8.5 mm. Endplate 1002thus has an endplate height (h_(E1002)) of about 1.5 mm. Bottom edges ofendplate 1002 are spaced at a distance x of about 5 mm from center c ofcore 1004. Pores 1027 have a major dimension (shown as pore widthw_(P1027)) of about 600 microns. Endplate 1002 and endplate 1006 may becoated with hydroxyapatite before or after assembly with core 1004. Inone example, endplates 1002/1006 are formed by diffusion bonding anymetallic components (i.e., a sheet forming core interface side 1028, asheet forming bone interface side 1026 and any barrier layertherebetween) together in a press shaped to produce a desired endplateshape or contour. Formed endplates 1002/1006 are spray coated withhydroxyapatite prior to placement in a mold, and core 1004 is injectionmolded into a cavity between endplates 1002/1006.

FIGS. 40-44 show device 1000 with threading 1015 applied to core 1004and endplates 1002, 1006. FIGS. 40-44 are best viewed together with thefollowing description. In one embodiment, core 1004 is injection-moldedbetween un-threaded superior and inferior endplates 1002 and 1006 (see,e.g., superior endplate 1002 as shown in FIG. 36), and threading 1015 isthereafter machined onto the outer, middle surface of cylindrical device1000. Thus, as shown in FIGS. 40-44, superior endplate 1002, core 1004and inferior endplate 1006 all include threading 1015. Threading 1015may be continuously applied over core 1004 and endplates 1002/1006, asshown in FIG. 40, eliminating the need to align threading 1015 onpreviously-machined endplates 1002, 1006 with threading of core 1004.

In one aspect, channel 1008A is machined through the diameter of core1004 and aligns superior and inferior endplate apertures 1010 and 1012,respectively. Channel 1008A is for example a narrow slot that opens intoand runs substantially perpendicular to channel 1008B through core 1004,and likewise runs substantially perpendicular to, and may intersect oneor more of, lateral channels 1008C-1008E within core 1004. Superioraperture 1010, channel 1008A and inferior aperture 1012 may be machinedthrough superior endplate 1002, core 1004 and inferior endplate 1006 ina single operation to create an opening for bone growth entirely throughdevice 1000. Optionally, endplates 1002 and 1006 are formed withrespective apertures 1010 and 1012 prior to placement in a mold, andchannel 1008A is formed via molding. Bone growing into device 1000through channel 1008A (via endplate apertures 1010, 1012) may spreadinto channel 1008B and portions of channels 1008C-E that are not blockedby fusion enhancing glue.

Endplates 1002 and 1006 are curved to conform to a desired shape (e.g.,a cylindrical shape) of core 1004 and to facilitate screw-type insertionat an implant site. Device 1000 length (l_(D1000)), shown in FIGS.42-43, is about 30 mm. Channel 1008A length (l_(ch)) and width (w_(ch))are about 22 mm and 6 mm, respectively. Lateral channels 1008C-1008Ehave a width (w_(lat)) and a length (l_(lat)) of about 4 mm. Aspreviously noted, diameter d of device 1000 may be about 20 mmconsistently, or may vary along device 1000, for example if device 1000tapers from end 1007 to end 1005.

It will be appreciated that although device 1000 is shown and describedwith one superior and one inferior endplate, device 100 may alternatelyinclude a plurality of endplates formed from titanium segments spacedabout the perimeter of device 1000, and oriented along the long axisthereof.

FIGS. 45-52 illustrate a generally kidney-shaped composite interbodydevice 2000 having superior and inferior endplates 2002 and 2006,respectively, on inferior and superior sides of a core 2004. Core 2004is made of a biocompatible material that is sufficiently malleable forforming in a desired shape, yet strong enough to meet durabilityrequirements of an intended implant site. In one embodiment, core 2004is for example PEEK plastic that is injected between endplates 2002 and2006 in a mold, and cooled to harden and bond. Alternately, superior andinferior endplates 2002 and 2006 may be press-fit with core 2004, bondedto core 2004 with a biocompatible adhesive, or mechanically attached tocore 2004 using lock-and-key features such as v-grooves, or fastenerssuch as small screws.

On an insertion side 2005, core 2004 curves outward to form a noseportion 2022 (see FIG. 46). Nose portion 2022 may facilitate insertionat an implant site (i.e., between adjacent vertebrae). Core 2004 has oneor more features 2008, such as apertures into or channels through core2004, for encouraging bone through growth. Feature 2008A is avertically-oriented channel through core 1004. Feature 2008B is anaperture through a back side 2007 of core 2004 (side 2007 is distal tothe spinal cord when inserted between vertebrae), which facilitatesinsertion of device 2000 into an implant site. Aperture 2008B is forexample sized to accommodate a selected insertion tool. One or more offeatures 2008 may optionally be packed with bone and/or other materialsto enhance fusion.

Aperture 2008B opens into channel 2008A. Three insertion-side apertures2008C-20008E through insertion side 2005 also open into channel 2008A.Features 2008C-2008E may be filled partially or completely withfusion-enhancing glue or other fusion aids. Optionally or additionally,features 2008C-E, and/or feature 2008B, facilitate bone growth throughcore 2004/device 2000. For example, bone growing through verticalchannel 2008A through device 2000 may encroach into features 2008B-Efrom within core 2004, where these features are not fully obstructed bya fusion aid. Features 2008A-D may be machined after core 2004 is molded(e.g., after injection-molding core 2004 between endplates 2002 and2006), or features 2008A-2008D may be extruded or otherwise formed.

As illustrated in the exploded view of FIG. 47, channel 2008A alignswith an aperture 2010 in superior endplate 2002 and with an aperture2012 in inferior endplate 2006 when device 2000 is assembled as shown inFIGS. 45 and 46. Where core 2004 is formed of radiolucent material, suchas PEEK plastic, one or more radio markers 2014 facilitate visualizationof core 2004 on x-ray, for example once device 2000 is implanted.Superior endplate 2002 bonds with a superior endplate contact surface2016 of core 304, and endplate 2006 bonds with an inferior endplatecontact surface 2018, as shown in FIG. 47.

As also illustrated in FIG. 47, endplates 2002 and 2006 include a porousbone-interface side 2026 and a porous core interface side 2028,separated by a barrier layer 2216, which is for example similar tobarrier layer 216 of endplate assembly 200. Porous metal sheets formingbone and core interface sides 2026 and 2028 may be diffusion bonded withbarrier layer 2216 therebetween, in a press shaped to lend any desiredcontour to endplate 2002 and/or 2026. Pores 2027 of bone interface side2026 are smaller than pores 2214 of core interface side 2028. Largerpores 2214 admit molten core 2004 material and facilitatecore-to-endplate bonding, while barrier layer 2216 prevents extrusion ofcore 2004 material into smaller pores 2027, which are reserved for bonein-growth. Pores 2027 may be sized for optimal bone in-growth; forexample about 600 microns in diameter or across a major dimension.

Alternately or additionally, as described above with respect to FIG. 25and device 300, endplates 2002 and 2006 may be machined with geometricfeatures protruding therefrom to increase relative endplate surface areafor bone on-growth on bone interface sides 2026. Endplates 2002 and 2006may be also be formed with ridges similar to ridges 313 of device 300(see FIGS. 23-27), thin webs or other geometric features, for examplefeatures resulting from plate fracture, to increase endplate surfacearea. Core interface sides 2028 of endplates 2002 and 2006 may also beargeometric features for increasing surface area of core interface sides2028, to enhance bonding with core 2004 material. It will be appreciatedthat endplates 2002 and 2004 may alternately be formed by metallic meshlayers separated by a barrier layer (as described above with respect toassembly 200), or by bonding a porous metallic layer with a titaniumsheet having ridges or other area-enhancing features on its oppositeside (as described above with respect to device 3000).

FIG. 48 is view of device 2000 from insertion side 2005, and FIG. 49 isa cross-sectional view along line 49-49 of FIG. 48. FIGS. 48 and 49 showfeature 2008D substantially aligned with feature 2008B, providing ahorizontally oriented (when device 2000 is implanted) channel completelythrough device 2000. Features 2008D and 2008B may be equal in size, asshown, or feature 2008D may be smaller than feature 2008B so that ansurgical tool inserted through feature 2008B will not fit completelyinto feature 2008D. In such a case, feature 2008B provides support foran insertion device while insertion side 2005, proximate feature 2008D,provides resistance necessary to advance device 2000 within an implantsite.

FIG. 50 is a bone-interface side 2026 view of either superior endplate2002 or inferior endplate 2006, showing additional detail of boneinterface pores 2027. As shown, pores 2027 need not be circular but mayinstead be square or rectangular (e.g., where formed by a metallicmesh). Other pore geometries are also within the scope hereof.

FIG. 51 is an end view of device 2000, showing feature 2008C visiblethrough feature 2008E. Device 2000 width (w_(D2000)), shown in FIG. 51(a rear-side 2007 view of device 2000), may be similar to width w_(D) ofdevice 100. Device 2000 length (l_(D2000)) and height (h_(D2000)), shownin FIG. 52, may also be similar to length (l_(D)) and height (h_(D)) ofdevice 100 (see FIGS. 2-3). In one embodiment, l_(D2000) is 20-30 mm andh_(D2000) is about 8-15 mm.

It will be appreciated that device 1000 or device 2000 may be formedaccording to the methods illustrated in FIGS. 29-33. In one alternateexample of method 500 (FIG. 29), inferior and superior endplates 1002and 1006 are assembled, in step 502, and placed in a mold with coreinterface sides 1028 facing a core cavity in the mold, in step 504. Corematerial 1004 is injection molded into the cavity and, through thecavity, into pores of the core interface side, in step 506. Note thatwhile core interface pores are not shown with respect to device 1000,they are within the scope hereof.

The endplate 1002-core 1004-endplate 1006 assembly is allowed to set(for example, the assembly may be cooled until core 1004 fully hardens),in step 508, and removed from the mold, in step 510. One or more offeatures 1008A-1008E are formed in interbody device 1000, in step 512.In one example of step 512, features 1008A-1008E in core 1004 andapertures 1010 and 1012 through respective endplates 1002 and 1006 areformed in device 1000. For example, one channel may be drilled throughdevice 1000 to form aperture 1010, channel 1008A and aperture 1012 (SeeFIGS. 40-41). Bone interface surfaces of the device (i.e., boneinterface surfaces 1026 of endplates 1002 and 1006) are coated withhydroxyapatite, in step 514. It will be appreciated that although shownas a final step in FIG. 29, hydroxyapatite may alternately oradditionally be coated onto bone interface surfaces 1026 prior to theirincorporation into endplates 1002 and 1006 (i.e., where endplates 1002and 1006 are formed in a multi-step process, as with assembly 200, FIG.19), or after formation of endplates 1002 and 1006 and prior toplacement in the mold.

In one alternate example of method 31, metallic wire mesh is selectivelylayered to form bone interface side 2026, in step 702. For example, oneor more sheets of titanium wire mesh is placed or layered to form boneinterface side 2026 of endplate 2002 and/or endplate 2006. Centralbarrier layer 2216 is formed from a solid metallic (e.g., titanium)sheet placed on bone interface side 2026, and core interface side 2028is formed from larger-weave metallic mesh, placed on central barrierlayer 2216, in steps 704 and 706. In one aspect, bone interface side2026 is formed by selectively placing together titanium wire mesh layers204 and 206 of assembly 200 (FIG. 19), such that bone interface pores2027 formed by openings in the mesh are at a desired orientation, onelayer relative to the other. As noted above, pores 2214 of coreinterface side 2028 are larger than pores 2027 of bone interface side2026, to reduce flow restriction on the core interface side for enhancedcore-to-endplate bonding.

Bone interface side 2026, barrier layer 2216 and core interface side2028 are diffusion bonded together, in step 708. If shaping is required(decision 710), endplates 2002 and 2006) are shaped from the boneinterface side/barrier layer/core interface side assembly, in step 712,and optionally coated with hydroxyapatite on bone interface sides 2026,in step 714. Step 714 is illustrated as a dotted box to indicate thathydroxyapatite coating may take place at other points in method 700, forexample at position 726 or elsewhere.

Endplates 2002 and 2006 are placed in a mold with bone interface sides2026 facing a core cavity, in step 716, and core material 2004 isinjection molded between the endplates, and allowed to extrude intopores 2027, in step 718. After setting (step 720), interbody device 2000is removed from the mold, in step 722, and endplate 2002/2006 and/orcore 2004 features are created, in optional step 724. For example, afterrough interbody device 2000 is removed from the mold, endplate apertures2010 and 2012 are formed in endplates 2002 and 2006, respectively, ifnot already formed; and channel 2008A and any of features 2008B-2008Ethat were not formed in molding are machined into core 2004. Forexample, apertures 2010, 2012 and channel 2008A are drilled throughdevice 2000.

Bone interface sides 2026 may be coated with hydroxyapatite after device2000 is machined with its desired features, after endplates 2002 and2006 are shaped from the bone interface side/barrier layer/coreinterface side assembly, or both. Alternately, the one or more mesh orperforated layers forming bone interface sides 2026 may be coated withhydroxyapatite prior to placing the layers together to Rhin boneinterface sides 2026, or bone interface side 2026 may be coated withhydroxyapatite prior to its placement with central barrier layer 2116.The depth and placement of hydroxyapatite coating may vary as a functionof an intended implant site.

While the present invention has been described above, it should be clearthat many changes and modifications may be made to the process andproduct without departing from the spirit and scope of this invention.For example, select or all components of the above-described devices mayprovide an inter-bone bridge used for bone fusions outside of the spine.Additionally, components of different endplates described above may becombined, without departing from the scope hereof.

What is claimed is:
 1. A composite interbody device, comprising: aplastic core with superior and inferior surfaces and one or morefeatures for permitting bone growth through the core; a metallicsuperior endplate having: a core interface side comprising a perforatedmetal sheet and being coupled with the superior surface, a boneinterface side comprising a perforated metal sheet opposite the coreinterface side for interfacing with bone of an implant site,perforations in the bone interface side forming a plurality of boneinterface pores for permitting bone growth therein, and a centralbarrier layer between the core interface side and the bone interfaceside; and a metallic inferior endplate having: a core interface sidecomprising a perforated metal sheet and being coupled with the inferiorsurface, a bone interface side comprising a perforated metal sheetopposite the core interface side, for interfacing with bone of animplant site perforations in the bone interface side forming a pluralityof bone interface pores for permitting bone growth therein, and acentral barrier layer between the core interface side and the boneinterface side; and a hydroxyapatite coating applied to the boneinterface sides of the superior and inferior endplates, for encouragingbone growth onto the endplates; wherein perforations in the coreinterface side are larger than the bone interface pores, the coreinterface perforations permitting molten material of the core to flowinto the core interface perforations, to enhance bonding of the core tothe superior and inferior endplates, when the core is molded between theendplates; and wherein the central barrier layer of the superior andinferior endplates prevents the molten core material from flowingthrough the superior and inferior endplates and into bone growth spacesprovided by the bone interface perforations, when the core isinjection-molded between the endplates.
 2. The device of claim 1, thesuperior and inferior endplates comprising titanium.
 3. The device ofclaim 1, the core features including a vertically-oriented channelthrough the core; the inferior and superior endplates each comprising anaperture through the endplate and opening into the vertically-orientedcore channel, for permitting vertical bone growth through the interbodydevice.
 4. The device of claim 1, the core interface side of theinferior endplate and the core interface side of the superior endplatefurther comprising at least one layer of titanium wire mesh; the meshproviding a plurality of additional core interface pores for acceptingmaterial from the plastic core to enhance bonding between the core andthe superior and inferior endplates.
 5. The device of claim 4, the boneinterface side of the inferior endplate and the bone interface side ofthe superior endplate further comprising one or more layers of titaniumwire mesh providing additional bone interface side pores; wherein theadditional bone interface pores are smaller than the additional coreinterface pores.
 6. The device of claim 5, the bone interface poresbeing about 600 microns.
 7. The device of claim 1, the bone interfaceside, the core interface side and the central barrier layer of eachendplate being diffusion bonded together to form the superior orinferior endplate.
 8. The device of claim 1, wherein the superior andinferior endplates are shaped to conform to one or both of (a) a shapeof the core, and (b) a shape of a bony contact surface at an implantsite.
 9. The device of claim 1, wherein a shape of the assembled deviceis selected from the group of a kidney-bean shape, a cylinder and abullet shape.
 10. The device of claim 1, the assembled interbody devicebeing shaped as a cylinder and having threading along at least a portionof its outer surface, for facilitating screw-type insertion of thedevice into an implant cavity.
 11. The device of claim 1, the superiorand inferior endplates each comprising a solid sheet of titanium formingthe central barrier layer between the bone interface side and the coreinterface side; the bone interface side and the core interface side ofeach endplate comprising micro-porous or micro-etched titanium layeredor formed on opposing sides of the central barrier layer.
 12. Acomposite interbody device, comprising: a superior endplate having: ahydroxyapatite-coated bone interface side for contacting bone of animplant site the bone interface side comprising at least one layer oftitanium mesh, wherein openings in the mesh provide bone interfacepores; the hydroxyapatite coating encouraging bone growth onto the boneinterface side, pores of the bone interface side permitting bone growthinto the bone interface side; a core interface side opposite the boneinterface side and comprising at least one layer of titanium mesh,wherein openings in the mesh provide core interface pores; a centralbarrier layer formed of a solid sheet of titanium between the coreinterface side and the bone interface side; and at least one aperturethrough the superior endplate; an inferior endplate having: ahydroxyapatite-coated bone interface side for contacting bone of theimplant site, the bone interface side comprising at least one layer oftitanium mesh, wherein openings in the mesh provide bone interfacepores; the hydroxyapatite coating encouraging bone growth onto theinferior endplate bone interface side; pores of the inferior endplatebone interface side permitting bone growth into the inferior endplatebone interface side; a core interface side opposite the bone interfaceside and comprising at least one layer of titanium mesh, whereinopenings in the mesh provide core interface pores; a central barrierlayer formed of a solid sheet of titanium between the core interfaceside and the bone interface side; and at least one aperture through theinferior endplate; and a plastic core between the superior and inferiorendplates and having: a superior surface bonded with and penetrating thepores of the superior endplate core interface side; an inferior surfacebonded with and penetrating the pores of the inferior endplate coreinterface side; and at least one channel through the core and alignedwith the superior endplate aperture at the superior core surface andwith the inferior endplate aperture at the inferior core surface, forpermitting bone growth through the composite interbody device; whereinthe bone interface pores of the superior and inferior endplates aresmaller than the core interface pores of the superior and inferiorendplates, to optimize the bone interface pores for bone in-growth whilereducing flow restriction on the core interface side, to facilitate flowof the core material into the core interface pores; the central barrierlayer preventing the core material from flowing into and obstructing thebone interface pores.
 13. The device of claim 12, the bone interfaceside of the superior endplate and the inferior endplate comprising atleast one layer of perforated titanium, wherein perforations in themetal provide additional bone interface pores; the core interface sideof the superior endplate and the inferior endplate comprising at leastone layer of perforated titanium, wherein perforations in the titaniumprovide additional core interface pores; and wherein the additional boneinterface pores are smaller than the additional core interface pores, tooptimize the bone interface pores for bone in-growth while reducing flowrestriction on the core interface side, to facilitate flow of the corematerial into the core interface pores; the central barrier layerpreventing the core material from flowing into and obstructing the boneinterface pores.
 14. The device of claim 12, wherein the core interfacesides of the superior endplate and the inferior endplate comprisemicro-porous or micro-etched titanium layered or formed on a first sideof the solid sheet of titanium, and the bone interface side of thesuperior endplate and the inferior endplate comprise micro-porous ormicro-etched titanium layered of formed on a second side of the solidsheet of titanium.
 15. A composite interbody device, comprising: aplastic core with superior and inferior surfaces and one or morefeatures for permitting bone growth through the core; a superiorendplate including a core interface side configured with the superiorcore surface and a bone interface side opposite the core interface sidefor interfacing with bone of an implant site; the bone interface sidebeing coated with hydroxyapatite and having a plurality ofmicro-machined surface features for increasing the bone interface sidesurface area, to enhance bonding between bone and the bone interfaceside; an inferior endplate including a core interface side configuredwith the inferior core surface and a bone interface side opposite thecore interface side, for interfacing with bone of an implant site; thebone interface side being coated with hydroxyapatite and having aplurality of micro-machined surface features for increasing the boneinterface side surface area to enhance bonding between bone and the boneinterface side; wherein the device is shaped as a cylinder and the micromachined surface features include threading, for facilitating screw-typeinsertion of the device into an implant cavity.
 16. The device of claim12, wherein a shape of the assembled device is selected from the groupof a kidney-bean shape, a cylinder and a bullet shape.